Method of centrifugally casting tubular bodies



Jan. 20, 1970 H. STEIN 3,490,135

METHOD OF CENTRIFUGALLY CASTING TUBULAR BODIES Filed Oct. 10, 1987 Aluminum Sand-pifved Surface {Cenfrifl1gdilg-Casi iron) Cenfrifuga/ly-casf Iron 73 u Coarse-grain Sand Q Qinder 14 r Fine-grain Sand Binder Cast-iron Mold Herberf Sfein INVENTOR.

Attorney United States Patent Thompson & Co. G.m.b.H., Frankfurt am Main, Ger-.

many, a corporation of Germany Filed Oct. 10, 1967, Ser. No. 674,210 Claims priority, application Germany, Oct. 11, 1966, 2

Int. Cl. B22c 1/52; B23p 17/00 US. Cl. 29-417 6 Claims ABSTRACT OF THE DISCLOSURE A method of making annular bodies wherein a tubular blank of iron is centrifugally cast in a mold lined witha mixture or large-grain sand particles and synthetic-resin binder whereby the metal penetrates into the interstlces of the lining, the lining being formed on a bed of finegrain sand particles and resin which permits the blank, upon withdrawal from the mold, to retain adherent largegrain sand particles without requiring the blank to have a draft or conical shape, the sand being thereafter removed to form a pitted exterior of the blank which can then be covered by another metal for highly effective binding and heat transfer thereto.

My present invention relates to a method of making tubular bodies, especially relatively long cylindrical bodies such as cylinder-bore lining sleeves, brake rings, etc. and, more particularly, to a method of centrifugally casting such bodies which may be covered subsequently with a layer of another metal.

The centrifugal casting process, whereby a molten metal is introduced into a hollow mold rotated rapidly about its axis to force the metal by centrifugal action outwardly against the wall of the mold, is already in common use for the production of generally tubular bodies which are to be coated or clad with a layer of another metal in heat-transfer relationship with the inner blank and must adhere strongly thereto. To provide a roughened, pitted or correspondingly contoured exterior of the blank, it has been suggested to provide a layer of relatively coarse sand particles along the wall of the mold; under the centrifugal action, the molten metal is forced into and penetrates the interstices between the sand particles so that, upon cooling of the metal, the projecting portions or protuberances between the sand particles form a roughened surface to which the subsequently applied layer metal is strongly adherent and, in effect, interfits. As a result, heat-transfer efiiciency across the interface is extremely high. The sand particles imbedded in the roughened surface of the blank can be removed by chemical techniques prior to the application of the outer layer. The casting process has been carried out with iron (and steel) and the coating metal generally is a light metal such as aluminum or an aluminurn alloy. The cladding or covering layer is found to be so strongly adherent to the inner body as to be able to withstand thermal and mechanical stresses, including vibrational and impact perturbations of the type arising in automotive-vehicles applications. Consequently, these methods have been proposed for the guide bushings or sleeves of internal-combustion-engine cylinders, brake rings, piston rings and the like.

In carrying out a process of this type, it has been found that a major technological disadvantage resides in the difiicnlty in withdrawing the solidified metal blank from the centrifugal-casting mold when the blank is a cylindrical body of relatively large length. In fact, by conventional techniques, cylindrical bodies cannot be withdrawn ICC from such molds and it has been necessary to shape the interior of the mold (and the exterior of the body) with draft or taper to permit withdrawal. When a relatively thick layer of large-particle-size or coarse-grain sand is used to line the mold, it is found that at least part of the sand is pushed by the incoming stream of molten metal along the mold and accumulates at the far end thereof and that only a small amount of the coarse-grain sand remains along the mold to assist in forming the roughened surface discussed earlier. It appears that this migration of the sand is a consequence of the fact that the coarse particles or grains do not cooperate in the layer to form a relatively immobile lining but rather rest against one another at so few points as to form, in effect, a multiplicity of movable elements. There is little adhesion between these particles.

It is, therefore, the principal object of the present invention to provide an improved method of making cylindrical or substantially cylindrical tubular bodies of the character described wherein the aforementioned disadvantages are avoided.

Another object of this invention is to provide an improved method of centrifugal casting metal bodies with uniformly roughened surfaces adapted to receive a further metallic layer.

I have found that these objects can be obtained by initially providing the inner wall of a centrifugal casting mold with a layer of relatively fine-grain sand particles and a synthetic-resin binder (e.g. a phenol-formaldehyde resin) while a layer of relatively coarse-grain sand adapted to form the pitted surface of the metal casting is provided with a similar binder along the first layer or bed. The latter layer forms, between the coarse-grain sand particles, interstices into which the molten metal penetrates to form the protuberances or projections mentioned earlier. The fine-grain sand has a substantially greater binding quality than the large-grain sand and therefore is strongly adherent to the interior of the mold and has little tendency toward brake up even with rotation of the mold. The layer of coarse-grain sand, in turn, adheres to the fine-grain sand layer much more strongly than it does to the cast-iron mold wall and thus does not migrate under -the action of the molten metal which is capable of thermally breaking down the binder whose purpose is merely to facilitate the application of the layer to the walls of the mold and is not intended to withstand the stress of the molten metal in se. The thermal destructibility of the binder during the casting process permits the cast body to be withdrawn easily from the mold.

An important advantage of this invention is that the cylindrical bodies with roughened surface produced by this technique can be made much longer than heretofore and, consequently, economically cut up into a plurality of shorter sleeves or rings. The finishing costs for articles of this nature can be reduced sharply and the drafts or tapers eliminated in their entirety.

The above and other objects, features and advantages of the present invention will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

FIG. 1 is a diagrammatic cross-sectional view through a portion of the mold according to this invention after the molten metal has been cast therein; and

FIG. 2 is an elevational view, partly broken away, showing an article as made by the present system.

In FIG. 1, in which the layers lining the mold have been disproportionally enlarged, I show a cylindrical castiron centrifugal-casting mold 10, whose inner surface 11 is lined with a layer 12 of fine-grain sand and syntheticresin binder. The fine-grain sand can be of the type conventionally used in green-sand casting, while the binder may be of any of the thermally destructible types common inthe casting of iron in sand moldsThus, a phenol- 7 formaldehyde resin and sand of a mesh size of 100 to 325 mesh may be used, the resin proportion in this layer being about 10% by weight of the layer. Ureaformaldehyde binders may also be employed. Atop the finegrain sand/binder layer 12, I provide a layer 13 of course-grain sand and binder, the latter being present in an amount of about 10% by weight. The coarse-grain sand should have a particle size (in terms of particle diameter) ranging from 10 to 50 times that of the finegrain sand and may be from 3 /2 to 35 U.S. mesh by Way of example; the casting and removal proceed in the usual manner. At the interface 14 between the coarse-grain sand/binder layer 13 and the bed 12, there is strong mechanical adhesion between the sand particles of the tWo layers and little tendency toward migration when the molten metal layer 15 of cast iron is poured into the mold. At interface 16, the molten metal, under centrifugal force and at a temperature sufficient to break down the ureaor phenol-formaldehyde binder, penetrates layer 13 and forms a sand-pitted roughened surface when the adherent sand is removed by conventional chemical techniques. This sand-pitted surface of the tubular cast iron blank is represented at 17 in FIG. 2 and is shown to be covered by a layer 18 of aluminum which penetrates into the pits and cavities of the blank 19 which may be cut up at 20 and 21 into brake or piston rings, cylinder-lining bushings for internal-combustion engine, or the like.

I claim: 1. A method of making tubular bodies comprising the steps of:

(a) lining a centrifugal casting mold with a first layer of fine-grain sand admixed with a binder; (b) covering said first layer with a second layer of relatively coarse-grain sand admixed with a binder; (c) centrifugally casting a tubular metal blank in said mold in contact with said second layer whereby the metal penetrates between the coarse-grain sand particles of said second layer; and i (d) removing said blank, upon hardening, from said mold and stripping any adherent coarse-grain sand particles therefrom to provide a roughened exterior surface of said blank.

2. The method defined in claim 1 wherein said metal is iron and the binder in at least said second layer is a synthetic resin thermally destructible at a temperature at which said blank is cast in step (c).

3. The method defined in claim 2 wherein said coarsegrain sand has a particle size ranging from 10 to times that of the fine-grain sand of said first layer.

4. The method defined in claim 2, further comprising the step of covering the surface of said blank with a layer of another metal.

5. The method defined in claim 4 wherein said other metal is aluminum.

6. The method defined in claim 4, further comprising the step of cutting said blank into a plurality of tubular bodies.

References Cited UNITED STATES PATENTS 1,745,835 2/1930 Merrill 29-417 X 2,255,896 9/1941 Projahn 1641 14 X FOREIGN PATENTS 1,269,898 12/ 1960 France.

1, 1 5 7,744 11/ 1960 Germany.

I. SPENCER OVERHOLSER, Primary Examiner I. E. ROETHEL, Assistant Examiner U.S. Cl. X.R. 

